The invention relates to a protective circuit for electronic modules, in particular driver modules, according to the preamble of claim 1.
It is generally accepted to employ protective diodes for the protection of electronic components against contusion of the poles of the supply voltage. For this purpose either a protective diode is inserted with proper polarity of the supply voltage in forward conducting direction into the feed line of the higher disposed supply potential (+Ub;Vcc) or into the return line of the lower disposed supply potential (xe2x88x92Ub; GND; 0 V). The load currents of all outputs of the component have to take the path to this protective diode in the first case, wherefore a correspondingly large dimensioned and thus expensive protective diode has to be furnished. This disadvantage does not occur in the second case, wherefore this disposition of the protective diode is to be preferred.
In connection with electronic components, in particular driver components, sometimes the case occurs that internal resistances exist between the outputs and the supply connection for the lower disposed potential. This lead to a so-called break or rupture of the neutral conductor, that is an interruption of the supply conductor for the lower disposed supply potential, to a parasitic current flow through the supply connection of the component, the internal resistances and the outputs and finally the loads to the lower disposed supply potential. Thus non-defined and unstable voltage levels, that is undesired voltage levels can occur at the outputs of the component, whereby the safety is not assured in case of a break of the neutral conductor.
Therefore it is an object of the present invention to combine an economic protection against reverse polarity with the protection against a rupture or break of the neutral conductor.
Starting from a protective circuit of the initially recited kind, the object is accomplished according to the present invention by the characterizing features of the independent claim, while advantageous further development of the invention can be gathered from the dependent claims.
It is effectively prevented by the arrangement according to the present invention of the known protective diode and a further protective diode, that in case of a rupture of a neutral conductor, currents can form through the internal resistances and the external loads. The component remains on the output side in a defined, that is secure state upon a rupture of the supply line for the lower disposed supply potential independent of the state of the input signals.
Only a single first protective diode is required independent of the number of the components concerned.
The use of the same damping diodes reduces the dependence of the circuit arrangement on forward voltages, forward currents, back blocking voltages, temperature behavior, frequency dependence, and the like in a decisive measure.